This invention relates to an arrangement for the working (finishing) of internal surfaces of metal parts in a cylindrical opening having a high slenderness ratio, possibly in a cylindrical throughgoing opening, wherein for performing such working an electrode connected to the negative pole of a source of burning electrical impulses is applied to the surface to be worked, the positive pole of such current source being conductively connected to the worked metal part.
The working of internal rotational surfaces--also called recessing surfaces--in cylindrical hollow spaces of metal parts and in cylindrical throughgoing openings therein presents substantial difficulties when hollow spaces or openings with the high slenderness ratio are involved. This is particularly so if the absolute value of the diameter of the cylindrical hollow space or of the opening amounts to several millimeters, as is the case for instance in the up-to-date injection nozzles of Diesel engines and the like.
Working by turning is difficult with a slenderness ratio D/L equal to 1/5, so that it is out of the question to apply it practially in such cases.
Working by grinding also fails when the slenderness ratio D/L is equal to 1/8.
It is possible to work or finish by electrolytical working of internal rotational surfaces at relatively substantial depths. There are, however, drawbacks, in that the worked surface is not accurate, the diameter and shape of the worked surface is somewhat dependent upon the working time, and a satisfactory coaxiality cannot be achieved. When working by the electrolytic method, a defective, so-called guiding diameter is usually the result, i.e. the diameter of the cylindrical surface, where the required rotational surface is created, so that it is impossible to achieve a sharp edge on the junction between the guiding diameter and the worked surface.
A rather inconvenient aspect of this working process is that remnants of the electrolyte can be removed from deep openings only with with difficulty, causing further complications with processes that follow, and influencing the final quality of the product.
These working methods involve the expenditure of a large amount of labor, which of course is not desirable economically.